Effect of tryptophan on growth, intestinal enzyme activities and TOR gene expression in juvenile Jian carp (Cyprinus carpio var. Jian): Studies in vivo and in vitro

Abstract

This study was conducted both in vivo and in vitro to investigate the effects of tryptophan on growth performance, digestive and absorptive function and protein synthesis of juvenile Jian carp (Cyprinus carpio var. Jian). 1050 juvenile Jian carp (initial weight 7.73±0.03g) were fed seven isonitrogenous diets with graded concentrations of tryptophan (1.1, 1.7, 2.5, 3.8, 4.9, 6.0, 6.9g/kg diet) for 8weeks. Percent weight gain, feed intake and protein retention value were markedly improved, with increases in dietary tryptophan up to 3.8g/kg diet. Similar trend was found in glutamate–oxaloacetate transaminase (GOT) and glutamate–pyruvate transaminase (GPT) activities, trypsin, lipase and α-amylase activities, Na+/K+-ATPase, alkaline phosphatase (AKP), γ-glutamyl transpeptidase and creatine kinase activities, and relative expression of eIF4E-binding protein (4E-BP). On the other hand, feed conversion ratio, plasma ammonia concentration and the relative expression of target of rapamycin (TOR) in different tissue showed an opposite pattern. A series of experiments in vitro were then carried out. Compared with the control group, tryptophan supplementation increased 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) OD value, protein content and activity of AKP, GOT, GPT and Na+/K+-ATPase in enterocytes and decreased lactate dehydrogenase activity and ammonia concentration in the culture medium. Protein synthesis rate was 17% higher and relative expression of TOR was 28% lower in tryptophan-supplemented than in control carp enterocytes. In conclusion, our results indicate that tryptophan improved fish growth, digestive and absorptive function as well as protein synthesis, which may be partly related to the TOR signaling pathway.